Occasionally I have to access the Application Data folder in XP. What is it? Simple answer: It is a place where programs cache information about user settings. Unfortunately, it seems rather easy to accumulate a lot of junk files in there as well. On my machine I have found a lot of files associated with programs I have uninstalled.
To see this folder open My Computer and click through the following sequence: “Tools”, “Folder Options…”, “View”, and finally “Show hidden files and folders”. You will need to be logged in as an Admin to do this.